Why isn't DIR universally metric?

[Kevrumbo]

That's unequivocally not unique to your unit system.

Metric / Imperial is a "who cares" type of a deal.

It's inconsequential.

To you it is . . . but very useful and obviously vital to those of us who understand this advantage of metric and can utilize it. . .

Please show and explain what you claim Marc, is inconsequential. . .

 

[mikemill]

So do all you metric folks do everything in seconds? Or do you use the easier to manage minutes?

 

[Blackwood]

To you it is . . . but very useful and obviously vital to those of us who understand this advantage of metric and can utilize it. . .

Please show and explain what you claim Marc, is inconsequential. . .

I can use either fluently. It doesn't matter to me, thus it's trivial. It's just little letters on a gauge (BAR or PSI).

Knowing what they mean and how they relate to your dive, on the other hand, is highly consequential.



Does being able to roll a decimal one way or another make multiplication/division simpler? Of course. Does it affect my diving? Of course not. Do I dive in even one atmosphere depth increments? Of course not.

Again, I dive my gauge, which will either say PSI or BAR. I have little need to think of volumes during the dive. Before the dive starts, I'll know my expected consumption rate in either PSI/atm/min or BAR/bar/min and my rock bottoms/turn pressures.

Introducing the parameter during the dive which doesn't show up on any instrumentation (i.e. volume) is only useful if I need to do computations on-the-fly about my team's gas, and if that's the case I'm we're likely ending the dive anyway. It's tantamount to converting the foot or meter on your depth gauge to the pressure which the gauge is registering.

 

[Kevrumbo]

If you claim fluency, then show what's dismissively trivial to you . . .what's there that's so commonly obvious & non-novel to you?

30m depth -->3bar/min or 30bar in 10min
or depth translates to pressure consumption rate.
(an easy relationship to utilize; what is trivial to you is so vital & useful to me). . .

 

[Blackwood]

If you claim fluency, then show what's dismissively trivial to you

The unit system.

what's there that's so commonly obvious & non-novel to you?

How tanks are rated (volume to pressure).

30m depth -->3bar/min or 30bar in 10min
or depth translates to pressure consumption rate.
(an easy relationship to utilize; what is trivial to you is so vital & useful to me). . .

In the tanks you usually dive and at the consumption rate you usually experience.

If you are in 15L doubles in cold water with two bottles, a scooter and current, what does your rule of thumb predict to be your consumption rate at 43m?

In the tanks I usually dive and at the consumption rate I usually experience, I consume about 10PSI/minute per atmosphere. If you are like me, you'll find 1PSI or 10PSI (or 1BAR) hard to read on an analog gauge, but 100PSI is easy, so I think in 10-minute segments. I expect to use 100PSI in 10 minutes per atmosphere. It's pretty easy. I can add percentages to taste for conservatism.

It's trivial because you can come up with these relationships in either system. It's the understanding that matters.

 

[Kevrumbo]

The unit system.



How tanks are rated (volume to pressure).



In the tanks you usually dive and at the consumption rate you usually experience.

If you are in 15L doubles in cold water with two bottles, a scooter and current, what does your rule of thumb predict to be your consumption rate at 43m?

In the tanks I usually dive and at the consumption rate I usually experience, I consume about 10PSI/minute per atmosphere. If you are like me, you'll find 1PSI or 10PSI (or 1BAR) hard to read on an analog gauge, but 100PSI is easy, so I think in 10-minute segments. I expect to use 100PSI in 10 minutes per atmosphere. It's pretty easy. I can add percentages to taste for conservatism.

It's trivial because you can come up with these relationships in either system. It's the understanding that matters.

Tanks in metric have a base water volume-to-standard-ambient-atmospheric-pressure rating (water being incompressible and standard ambient atmospheric pressure at sea level is 1atm or 1.01bar); the most common tank used at dive-ops worldwide is the 11 litre/bar (the ubiquitous AL80). Fill it up to full rated pressure of 200bar and you have (11)(200) equals 2200 litres of gas. Straightforward, intuitive, makes sense, easy to implement but definitely non-trivial.

For your example of double 15L tanks (30L total), cold water (my cold water volume SCR is 22L/min*ATA or 0.75cf/min*ATA), at 43m depth:
43m is -->4.3 bar/min or 43bar consumed in 10min (Scootering). Therefore I would expect my SPG to read in the vicinity of 40 to 45bar delta down from my previous reading. So if my previous reading was 190bar ten minutes ago, I would expect the reading to be now around 145 to 150bar (i.e. I can't read 1bar increments either, nor is it really necessary to read your gauge with that much precision).

If I stow the scooter and start finning around instead, I'll figure my consumption to be approx 30% more, or alternatively, utilize the depth to pressure rate relationship this way: 43m is 5.3ATA -->5.3bar/min or 53bar consumed in ten minutes.

It's the understanding of how to manipulate these figures easily and expeditiously in problem solving, to your advantage . . .for whatever unit system. That's what matters and it's never trivial.

 

[Rainer]

It's the understanding that matters.

But that's his problem.

 

[AndyNZ]

But that's his problem.

Personally, I think that's a little unfair and mostly unwarranted.

Why spoil a good discussion with a pointed jibe?

 

[Kern]

Metric / Imperial is a "who cares" type of a deal.

I have to agree, its a "who cares" situation.

 

[Kevrumbo]

"Who cares" ???

Your buddy cares if you've gotta get him out from an overhead, in an out-of-gas contingency: Imperial or Metric, you better have figured the correct amount to get you both out & up to the surface (or at least to your deco gas switch). . .